The present invention relates to fluid flow control devices for controlling the discharge of a fluid from a discharge port in a fluid conduit. The invention is particularly useful in drip irrigation drippers included in a water irrigation pipe for controlling the flow of irrigation water to plants to be irrigated, and is therefore described below particularly with respect to such an application.
The present invention is especially useful in drip irrigation emitters that provide a very low flow-rate while operating under an ordinary range of line pressure. The emitters disclosed in the present application are capable of discharging a flow rate as low as 0.25 L of water per hour, whereas prior art drippers are generally not capable of achieving flow rates of less than 1.2 L per hour, under such line pressure. The present invention also provides a construction which allows manual flushing the emitter passageways when clogged by solid particles or other substances.
For many years, drip emitters have been used for delivering localized, low flow irrigation to the roots of plants. Directing water drops to the vicinity of each plant was proven effective to conserve water and also to prevent soil erosion. A variety of drip irrigation devices are available, mostly for operation under an ordinary range of line pressures which, for irrigation applications, is generally 1.5 to 4 bars, to produce emitting flow rates of 1.2 to 8 L/hr. Selection of an appropriate flow rate depends on the plants and the type of soil.
The evolution of drip irrigation led to the development of micro-drip systems designed for discharge rates below 0.3 L/hr. Various studies proved that in addition to its better water savings, the micro-drip method created a wider wetting bulb with better water/air ratio in the soil and no salinity in the root zone. In other words, micro-drip irrigation supplies water at a rate close to that of plant water uptake and therefore improves yields with reduced water losses by drainage below the root zone. An example of such a study is provided in Assouline, Cohen, Meerbach, Harodi and Rosner, “Microdrip Irrigation of Field Crops”, Soil Science Society of America Journal 66:228-235 (2002).
Prior art micro-drip irrigation systems used very low water pressure, in the range of 0.1 to 0.3 bar, to reach the required low emitting rate. This was done by using either pressure reducers or a water tank located at the proper elevation over the ground. An example of a system operating at low pressure from a water tank is described in R. Golan et al U.S. Pat. No. 7,048,010. Another example, related to a micro-drip system operating with pulsator devices acting as pressure reducers, is disclosed in P. Rosenberg U.S. Pat. No. 5,353,993
Generally, in use, ordinary drip emitters are placed along water feed lines such as 16 or 20 mm PE (polyethylene) tubes. The emitters may be plugged into discharge ports in the tubes, or may be inserted inside the tubes during the manufacturing of the drip lines. In any event, to accomplish small emitting rates, ordinary drip emitters rely either on small orifices to limit the flow rate, or on a labyrinth path designed to reduce the water pressure and accordingly the emitted flow rate.
Simple orifice emitters often become clogged by particulates in the feed line, or by the formation of sediments. The orifice diameter is therefore the major reason that prevents prior art designs from achieving emitting flow rates in the micro-drip regime under ordinary pressure. Simple labyrinth emitters are mostly made with wider passageways. However, the restriction to flow along the labyrinth path does not create enough pressure drop as needed for the emitter to maintain a discharge in the micro-drip regime.
Some recent designs combined both the orifice and labyrinth techniques, together with a flexible membrane, to construct a pressure-compensated drip emitter for achieving better discharge uniformity along the lines. This design concept is based on creating a constant pressure difference across the membrane, wherein the direct line pressure forces the membrane to close the orifice, and a reduced pressure from the labyrinth forces the other side of the membrane to open the orifice. However, the orifice in this configuration is located in series with the labyrinth; therefore this design is still sensitive to clogging.
More recent designs include a self-cleaning feature in the pressure compensating drip emitter. This feature is mostly attained by introducing a labyrinth path to produce a reduced water flow, and flushing the orifice before the pressure-compensating membrane is deformed to the extent needed to close the orifice and to start the normal dripping mode. Examples of a pressure compensating emitters that uses a reduced-pressure water from the labyrinth to clean the orifice during initial pressurization of the irrigation line, are disclosed in Bolinis et al. U.S. Pat. No. 6,464,152 and in Miller U.S. Pat. No. 5,628,462. In the latter, emitter, during initial pressurization of the irrigation line while the membrane is only slightly deformed, the orifice is flushed with reduced-pressure water delivered from the restrictor or labyrinth. Unfortunately, the orifice is subject to clogging by particulate buildup that might also interfere with the membrane seal, and therefore the reduced pressure water may be ineffective for adequately cleaning the orifice and membrane.